Definition of the utility of the Arrhenius method in the study of thermal stability of phenolic compounds in Urera laciniata Goudot ex Wedd

Abstract

The thermal degradation of the natural active principles is one of the most relevant topics in the stability of phytopharmaceuticals. For this reason, it is important to determine if a pharmaceutical formulation is adjusted to the behavior of the synthetic drugs and if the method of determining the time of shelf life is adequate. In order to establish whether the climatic zone criteria can be applied to the stability study by using differential scanning calorimetry, the experimental condition for the determination of the temperature at which the total ethanolic extract of Urera laciniata degrades was standardized. Furthermore, under this condition, the influence of the excipients on the variation of the degradation temperature in a solid pharmaceutical form was defined. It was found that the dry ethanolic extract has an average degradation temperature of 133.17 ± 0.84 °C and the excipients used raise this temperature by 54.87%. To verify the applicability of the Arrhenius equation in the evaluation of the shelf-life of the phytodrug, a stability study was carried out at 40 °C and 75% humidity. Through the quantification of total phenols in the dry ethanolic extract and in the pharmaceutical tablets, it was established that there are no significant variations that allow the calculation of the kinetic constant making the Arrhenius method inapplicable for the determination of the half-life time of the phytomedicine, and therefore, evaluation criteria using climatic zones cannot be used either.